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The Vaginal Microbiome




Our little tour of the microbiome of our body continues! After exploring the diversity of micro-organisms that are naturally in your digestive system, let’s learn more about the microbiota of our vagina! Let me start by saying that the vagina is a very clean organ: as you saw in the gut, having micro-organisms somewhere in your body is absolutely normal and definitely not dirty! In fact, the bacteria and other organisms help in our body processes and help maintain a normal environment. If the bacteria go out of balance, this may lead to different issues. Read more to understand the microbiota of the vagina and how to help stay in good balance!


Where the digestive system is full of a multitude and a variety of micro-organism, the vagina is a more of a select club, not allowing as many species to establish residence in the mucosa. The most common micro-organisms in the vaginal mucosa are a type of bacteria called Lactobacilli. Interestingly, these are similar bacteria to ones used to ferment milk into yoghurt (hence the name lacto!). These bacteria form the large majority of the healthy microbiota, and a disbalance can lead to several problems we will explain later. Indeed, these bacteria have a very important feature: they are little factories busy producing lactic acid. The presence of lactic acid causes the pH of the vagina to be very acidic, a pH around 4.5. In this environment, other bacteria trying to settle in the vagina will not feel welcome and will be prevented from causing trouble. Additionally, healthy resident bacteria produce anti-microbial peptides, directly killing other micro-organisms. So the “good” bacteria are again helping the body to fight off the “bad” bacteria!


The population of resident bacteria varies between different women and in the same woman across her life. This will depend on internal factors such as genes, immune mechanism and hormones, as well as external factors such as cleaning products and clothing. Indeed, recent research in healthy women has shown different possible pre-dominant species in vaginal microbiome, and these differences seemed to be associated with ethnicity. All the women studied had low diversity of resident bacteria and the predominant bacteria was either a species of lactobacillus or other healthy bacteria. Secondly, female hormones more specifically oestrogen have an important effect on the vaginal microbiota. This is through a well-understood mechanism, as oestrogens drive the production of a certain molecule in the vaginal mucosa, a molecule that feeds the lactobacilli but not other unwanted bacteria. This is why after menopause, where levels of oestrogen drop, the microbiota goes through important changes, the lactobacilli usually decreases in proportion and women may experience more infections in the vagina. Conversely, during pregnancy, where women have high levels of oestrogen, their vaginal microbiota has been measured to be healthier, with high proportions of good bacteria and low numbers of other intruding bacteria.

So what happens when something is “not quite right down there”? Sometimes, the micro-organisms in the vagina go out of balance or some “bad bacteria” can start to grow in large numbers in the mucosa. This causes the conditions named thrush and bacterial vaginosis. Thrush is when a certain type of yeast, named Candida albicans, that may be naturally present in the vagina in small numbers suddenly starts increasing in numbers. Low numbers of candida don’t cause any problems, but it is the sudden increase that can cause local inflammation and symptoms of thrush: itchy genital area and white discharge. Thrush is treated with oral medication and cream for the vulva, or a pessary inserted in the vagina. These will try to bring the yeast under control, to very low numbers again. Factors triggering thrush can be stress, hormonal changes and others.


An important risk factor for thrush is washing the genital area with products, as these can be very aggressive and harm the lactobacilli. Furthermore, the pH of the soap will completely disturb the natural acidic pH of the vagina. This is even worse when vaginal douching is performed, that is putting products inside the vagina to clean it. The very important point here is that most products sold to wash the genital area are not useful, the vagina is able to cleanse itself naturally, and adding any chemical product or soap in this area can disturb the natural balance of the microbiota, and cause infections! You should be washing your vulva with water only and the rest of your body with your usual soap unless your doctor instructs you otherwise. Putting water directly inside the vagina is not indicated at all, it will have no benefit and may actually disturb the balance again.


Additionally, oral antibiotics for other infections can also trigger thrush: these harm the “good” lactobacilli in the vagina, causing a breach in the normal defences and letting the yeast grow out of control. However getting on top of the infection will be the priority, in this case, so make sure you take the antibiotics if and when prescribed. Of course, don’t take any antibiotics if not prescribed, vaginal thrush is another reason why! Finally, some research has been done on the relationship between the vaginal microbiota and the digestive microbiota, as the exit of the digestive system is near the vagina. Certain digestive populations inpatient could possibly be associated with recurrent thrush.


Bacterial vaginosis (BV) is when an abnormal population of bacteria overgrows in the vagina. Numbers of bacteria increase quickly, as well as the different types of bacteria: the lactobacilli are not dominant anymore. This can cause symptoms of white or grey discharge, with a strong fishy odour. Burning on urination may occur but the itching is rarer. See your GP if you start getting such symptoms, they will be able to investigate and help you! Risk factors for BV are similar to those of thrush. The doctor may examine you and take a sample to look for the bacteria causing the infection, treatment will be with antibiotics.


There are some possible complications with BV that are not present with thrush. Sometimes the infection can rise up into the uterus and into your body, which can be very dangerous. This is called pelvic inflammatory disease and can be very serious. Signs are usually a pain in your pelvis, fever and feeling unwell. Seek urgent medical attention if you notice these! This remains rare but it is something to be aware of. Another problem with BV is that it increases the risk of catching other sexually transmitted infections, such as HIV, chlamydia and gonorrhoea. This is because the mucosa is inflamed and the natural defences are down.

Thrush and BV are not sexually transmitted diseases, and are common in many women, including many who may have recurrent infections. It is important to speak to your GP if you notice these symptoms, as treatment can be given to help you! It is not something you should be ashamed of talking about with your GP, and remember that having those infections don’t mean you have done something wrong. The GP sometimes refer women to the sexual health clinic because they have better equipment to investigate such infections, such as microscopes or swabs and are specialised in genital problems. This does not mean you have a sexually transmitted disease, though the GP may want to check for one just for extra safety. Some sexually transmitted illnesses can have symptoms that overlap with thrush or BV so checking will be able to reach a better diagnosis? Sometimes, there is no obvious cause to thrush or BV and it may not reoccur. In women with recurrent infections, probiotics can be tried to try to promote a good population of bacteria in the vagina. These have not been proven scientifically as of yet so do not feel you have to spend money on them! Research is still ongoing.


To finish this article, I want to mention the vaginal microbiota in the context of pregnancy. At birth, when the baby comes out through the vagina, this will be his first encounter with micro-organisms! In the large majority of cases, the vaginal microbiota causes absolutely no problem and is, in fact, vital to help your baby grow his own bacterial population is his own digestive system. Some babies born by c-section have been shown to have a different population of bacteria as they did not benefit from going through the vagina during labour. However, the populations of bacteria in your baby normalise quickly over time, without any treatment needed.


Some problems can arise due to infections during pregnancy. In a pregnant woman, certain bacteria can rise from the vagina to the uterus and can be associated with an increased risk of pre-term labour. This remains rare, but it explains why certain women whose water break too early will receive antibiotics in a drip during their labour. This is a decision the medical team will make as it may not be indicated in all cases. Furthermore, during vaginal birth, certain unwanted bacteria could cause infections to your baby. This is the case for example of a bacteria called group b strep. This is a common bacteria (20-40% of women) and the majority of babies are born safely without any infection. It should not be a cause of alarm if you are pregnant, but something the medical team may want to be aware of. The UK does not routinely test for group b strep in all pregnant women, but this can happen in some specific cases. This can be another reason for having antibiotics given during labour. If you are worried about any of these during your pregnancy you can discuss with the midwife or doctor following you. If you have symptoms of thrush or BV during your pregnancy, go visit your GP as they will give you different medications to remove the infection without harming your baby. The usual medication given over the counter at your pharmacy is contraindicated if you are pregnant.

Written by: Marianne




Disclaimer: Information in our blogs are as accurate and a comprehensive as possible. This is general advice and should not be used as a substitute for the individual advice readers might receive from consulting their own doctor. For other medical professionals reading, it is advised to use your own clinical judgement when interpreting the information and deciding how to best apply this to the treatment of their patients. Please see our terms and conditions page for further information on this.

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